Add PR 1106 GroupedRadio separator behavior to GroupedCheckbox

[freemansoft]

Connection with issue(s)

Close #1345

Connected to #???

Solution description

1. Copied GroupedRadio separator behavior into GroupedCheckbox.
2. Added to example app.
3. There was no test of the GroupedRadio behavior so don't know if you want a test.

Screenshots or Videos

To Do

• Read contributing guide
• Check the original issue to confirm it is fully satisfied
• Add solution description to help guide reviewers
• [] Add unit test to verify new or fixed behavior
• If apply, add documentation to code properties and package readme

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (66d87f0) 87.03% compared to head (caa0699) 87.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1346      +/-   ##
==========================================
+ Coverage   87.03%   87.71%   +0.68%     
==========================================
  Files          21       21              
  Lines         748      757       +9     
==========================================
+ Hits          651      664      +13     
+ Misses         97       93       -4     

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